1. Technical Field
This invention relates generally to hydraulic reservoirs used for supplying hydraulic fluid to hydraulic pumps, and more particularly to the means of handling the fluid returned to the hydraulic reservoir used to feed the pump under high flow, high pressure conditions.
2. Background of the Invention
Fixed and/or variable positive deplacement hydraulic pumps have numerous applications in many fields, including automotive, aerospace, industrial, agricultural, heavy equipment and the like for performing work. In a typical hydraulic system, return fluid is simply returned into the pump reservoir where it dwells for time period before being drawn in by the inlet to the pump for recirculation. Under conditions of high load and high flow rate, such hydraulic systems are characteristically unable to keep up with the fluid demand of the pump, leading to cavitation and unacceptable levels of noise. Another inherent disadvantage with such systems is that the kinetic energy of the incoming fluid to the reservoir is lost and not utilized to feed the inlet to the pump, leading to relatively low efficiencies. Such simple single return hydraulic fluid return systems thus have their limits.
U.S. Pat. No. 5,802,804 discloses a hydraulic steering system for a motor vehicle having two separate fluid return lines leading to the reservoir. One line is a high return flow which is fed to a nozzle within the reservoir. The outlet of the nozzle is supported adjacent the inlet to the steering pump. The momentum of the return fluid exiting the nozzle creates a venturi reaction at the reservoir outlet, which has the effect of aspirating additional volumes of fluid from the reservoir into the flow. The momentum of the return fluid together with the addition of the entrained fluid from the reservoir produces a desirable xe2x80x9cboostxe2x80x9d effect which provides ample feed to the pump under condition of high flow and high pressure to prevent cavitation attributed to lack of sufficient inflow to the pump. The second return line delivers a fraction of the return fluid to the reservoir. Such fluid is permitted to dwell for a time in the reservoir chamber, during which time any undesolved air or gas bubbles contained in the secondary stream are liberated before the fluid is drawn in by the primary jet stream. Without the second return line, the fluid would not be sufficiently deaerated and cavitation and noise would result.
U.S. Pat. No. 6,390,783, which is commonly owned by the assignee of the present invention, discloses a hydraulic system having a single fluid return line leading into the reservoir rather than the two separate fluid return lines of prior systems. This single fluid return line extends into a chamber of the reservoir and has a nozzle at its end adjacent the outlet of the reservoir which serves to direct a high velocity jet flow of hydraulic fluid from the nozzle through the outlet, causing a xe2x80x9cboostxe2x80x9d of additional hydraulic fluid to be drawn into the stream from the chamber to supply the pump with ample volume and pressure of fluid. A bleed hole is formed in the nozzle which allows for a controlled flow of the incoming fluid to escape or lead directly into the reservoir chamber through the bleed hole, where it dwells for a time before being drawn out of the reservoir by the jet flow issuing from the nozzle. As the fluid dwells, any air contained in the fluid is allowed to escape and, over time, has the effect of controlling or managing the aeration of the fluid contained in the system, such that the overall aeration levels remain below the upper limits which would cause cavitation or performance definicies of the pump. In order to promote an extended dwell time of the fluid issuing from the bleed hole, the reservoir is formed with a baffle which partitions the chamber and isolates the bleed flow for a time before mixing with the other fluid in the chamber. Such baffling, however, increases the complexity and cost of manufacturing hydraulic reservoirs in places design restrictions on the size and arrangement of the reservoir and its components.
It is an object of the present invention to further improve such hydraulic return flow reservoir systems, particularly in connection with the handling of the return flow to promote effective and efficient deaeration.
A hydraulic fluid reservoir for a hydraulic power system according to the invention includes a reservoir housing having an internal chamber for containing a supply of hydraulic fluid. The housing has an outlet for communicating fluid from the housing to an inlet of a hydraulic pump, and a return flow inlet for receiving a return flow of fluid into the chamber. According to the invention, the reservoir includes a flow diffuser having a diffuser inlet communicating with the return flow inlet of the housing for receiving at least a fraction of the return flow into the diffuser. The diffuser has an inner fluid guide wall that diverges in a downstream direction and which is operative to slow the velocity of the at least fraction of the return flow received into the diffuser through controlled expansion of the cross-sectional area of the at least fraction of the return flow as it advances along the diverging inner fluid guide wall of the diffuser. The diffuser includes a diffuser outlet communicating with the chamber for introducing the slowed velocity hydraulic fluid into the chamber.
One advantage of the invention is that the diffuser can be engineered to more precisely control the deaeration of the hydraulic fluid returning to the reservoir.
The controlled shape of the diffuser has the further advantage of dissipating turbulence of the fluid entering the diffuser as the fluid travels along the length of the diffuser such that upon existing the diffuser the flow is non-turbulent and the fluid is deaerated as it mixes with the bulk of the other fluid contained in the chamber of the reservoir.
According to a further preferred feature of the invention, the diffuser preferably has a conical form with an inside angle between walls no greater than 15xc2x0, such that the fluid entering the diffuser flows in contact with the conical wall with a constantly increasing cross-sectional area, decreasing the velocity of the flow and quieting any turbulence before the fluid exists the diffuser into the chamber. During this time, any air present in the fluid is released.
The invention has the further advantage of eliminating the design constraints associated with providing a baffle or deflector within the chamber as in prior systems. With the diffuser, there is no need for a baffle.
Another advantage of employing the diffuser according to the invention is that the diffuser is open and not subject to blockage or plugging as can be screens and other devices used to slow fluid flow.